Dosage counter for metered dose inhaler (MDI) systems using a miniature pressure sensor

ABSTRACT

A method and apparatus for directly counting the number of doses expended from a Metered Dose Inhaler (MDI) medicinal delivery system. A miniature pressure sensor and microprocessor is used to detect the pressure pulse in the transfer channel of the mouthpiece of the MDI through which the inhaler dose (the prescribed mixture of aerosol propellant and medicinal drug) is released. The microprocessor processes data reflecting the dynamics of the pressure pulse and counts the number of doses administered. The microprocessor displays the counted doses (or doses remaining) on a miniature digital display. Additional information also may be provided to a user from the display or via an audible signal.

BACKGROUND OF THE INVENTION

A Metered Dose Inhaler (MDI) is a pharmaceutical delivery system that iscommonly used to administer inhaled prescription drugs to treat avariety of conditions, including bronchospastic conditions such asasthma. MDI products contain aerosols which are generally solutions,primary emulsions, or suspensions of the active constituent along withpropellant contained in a pressurized canister.

A conventional MDI consists of: 1) a canister, usually made of metal,approximately two inches high and one inch in diameter, 2) a metereddose valve and dispensing nozzle that is affixed to the top of thecanister and is used to deliver a fixed quantity of the dose when thenozzle is depressed, 3) a plastic cap (the "mouthpiece") that is used toactuate the dispensing nozzle and to direct the dose into the patientslungs through the mouth; and 4) the contents of the canister, whichusually consists of a mixture of an aerosol propellant and drug that ismixed or suspended in the propellant. The aerosol propellant acts as acarrier medium to deliver the drug. A propellant may be a single aerosolor a mixture of aerosols.

At room temperature, the aerosol propellant creates a saturated vaporpressure inside the canister. Upon actuation of the device, the internalpressure in the canister forces a metered quantity of liquid through thevalve orifice and atomizes the actuated material. The pressure must beadequate to propel a metered quantity of the dose (propellant andmedicinal drug) out of the canister each time the MDI is actuated,creating a plume or "puff". The expended dose passes out of the meteringnozzle, through a small "transfer" channel in the plastic cap, and intoa delivery channel that directs the dose into the patient's mouth. Thepatient inhales the administered dose while depressing and thenreleasing the cap (mouthpiece) of the MDI so as to actuate the metereddose delivery.

MDI products currently offer the benefits of bronchodilator, steroid,and other drug delivery with less systemic effects than would normallybe observed following intravenous therapy. The MDI products also may beapplied to the delivery of drugs such as Leukotriene antagonists as wellas proteins and peptides.

The effective dose of drug delivered from a MDI product should beadequate and reproducible from actuation to actuation when treating apatient with asthma. For example, inappropriate and variable doses ofbronchodilators during an acute asthmatic attack can havelife-threatening consequences. Moreover, corticosteroids are oftenadministered chronically to patients with asthma as a prophylacticmeasure and a high degree of dose-to-dose uniformity offers the greatestamount of protection. Two major determinants of the effective dose whicha patient receives from a metered dose inhaler product are the dosedelivered from the MDI, as well as the size of the particles inhaledinto the pulmonary system.

Another consideration is that MDI pharmaceutical manufacturers typicallylabel the packaging and/or the MDI with a "labeled dose", which is themaximum number of doses to be used. MDI products typically containoverfill to ensure good dose to dose reproducibility for the number of"labeled doses" of the product. For these reasons, it is essential thatthe device delivers an accurate and consistent dose from actuation toactuation from the first until the "labeled dose" is reached. It is alsoimportant that the particle size is maintained at a level acceptable topenetrate deeply into the pulmonary tree for maximum efficacy. Thecurrent manufacturing practice of overfilling MDI products permitsactuation of the MDI well beyond the "labeled dose". When the "labeleddose" is exceeded, the dose strength could result in suboptimal therapy.

There are no easy, reliable ways currently available to the patient todetermine when a canister's "labeled" contents have been consumed andthat the patient has reached the "labeled dose". Typically patients willuse metered dose inhaler products until the entire canister isexhausted. This could represent 25% or greater actuations beyond thatlabeled for this pharmaceutical product. Thus, a mechanism which wouldaid the patient in tracking the number of actuations which have beenused for a given canister would aid the patient in determining when anMDI canister should be discarded and a new MDI canister used. Thedevelopment of such a device would enhance the ability of a patient tocomply or adhere to a prescribed dosing regimen. It is well appreciatedthat failure to adhere to medication dosage regimens can have a"profound influence on health care outcomes". (Levy; Pharm. Res. 12, No.7: 943-944, 1995).

Any improvement in the treatment of asthma could result in reducedhospital stays and reductions in related health care costs. From apharmacoeconomic standpoint, this would be highly desirable and thirdparty insurers would likely provide reimbursement for the added cost ofinnovations which could reduce the cost of treating this disease in thehospital.

One approach to identifying each actuation of a MDI and to determiningthe number of actuations for a given canister is seen in U.S. Pat. No.5,020,527 (Dessertine). However, the actuation of the MDI is identifiedby the mechanical operation of a lever each time the canister isdepressed for delivery of a dose, and the number of actuations of thelever is counted. This approach is deficient because the requirement fora mechanical actuation of a switch presents the greater possibility offalse actuations or failed actuations, thereby providing erroneousreadings.

Accordingly, the invention is concerned with the solution of these andother problems presently encountered in the art.

SUMMARY OF THE INVENTION

The present invention involves the use of a pressure sensor to measurethe pressure changes in the transfer channel of the mouthpiece of aMetered Dose Inhaler (MDI) medicinal delivery system. Pressure changesmay result from one or both of the dispensing of a dose and the inhaleprocess of a patient, or may also result from the effect of otherevents.

It is, therefore, the main object of the present invention to provide amethod, and an apparatus associated therewith, by which the number ofdoses consumed in a MDI system are counted for the purpose of assistingpatients in complying with prescribed use.

It is also the object of the present invention to provide a method ofcounting the number of doses consumed in a MDI medicinal delivery systemusing conventional technology that is readily available at low cost.

It is another object of the present invention to provide a method ofcounting the number of doses consumed in a MDI medicinal delivery systemin a direct manner of measuring the pressure rise and fall (the pressurepulse) within the transfer channel of the mouthpiece of the MDI as adirect result of the transfer of a dose, thus measuring the physicalevent of dose transfer to the patient, and avoiding indirect methodssuch as mechanical counter approaches which do not actually verify thata dose was administered.

It is another object of the present invention to provide a method ofcounting the number of doses consumed in a MDI medicinal delivery systemin a reliable manner by measuring the pressure pulse within the transferchannel of the mouthpiece of the MDI by using decision making softwarethat can be programmed to prevent false dose counting.

It is another object of the present invention to develop low cost modelsthat may be disposed of with each prescription and, also, to developmore elaborate models that would be more advanced in additional featuresand would be reusable.

It is another object of the present invention to embody other commoncapabilities of available low-cost microprocessors so that additionalfeatures may be added that will assist the patient in adhering toprescription requirements, including, but not limited to, standardcapabilities of microprocessors to store data, to perform programmedlogic, to measure time and to display messages or provide alarms.Features such as the display of the elapsed time since the last dose, orthe display of messages such as "shake before using", or "Use ONLY 100doses" could assist the patient in complying with the prescriptionrequirements.

It is another object of the present invention to embody other commonfeatures of microprocessors that would be readily available with thisinvention by adding components to the microprocessor that will assistthe patient in adhering to prescription requirements, including, but notlimited to, common capabilities of microprocessors to activate add-oncomponents such as a miniature speaker (to beep), or, to measure theoutput from a piezoelectric sensor or other motion sensing device tosense motion (as when the patient shakes the MDI, or does not shake theMDI, or does not shake the MDI long enough) so as to assist the patientin complying with the prescription requirements.

It is another object of the present invention to provide a method ofcounting the number of doses consumed in a MDI medicinal delivery systemto embody the spirit and scope of sensing the pressure rise and fall (orpressure pulse) in the transfer channel to similar applications of MDItechnology such as nasal dose applications, and even topicalapplications of medicines.

These and other objects are achieved by providing a mouthpiece for anMDI that uses a pressure sensor and by detecting changes of pressurethat occur when a drug dose is properly delivered. The pressure sensoris positioned to detect the pressure in the transfer channel or thedelivery channel of the mouthpiece of an MDI, and to identify theexistence of pressure changes. The pressure sensor is connected to amicroprocessor.

The microprocessor is programmed at least to determine the existence ofa pressure pulse and to count the detected pressure pulses in themouthpiece. An adequate threshold voltage for sensing the pressurepulse, over a determined period of time, is used so as to defineconditions that would equate to a "Counted Dose". The algorithm used bythe microprocessor is programmed to eliminate the occurrence of falsecounts and missing counts and thus make the recording of doses reliable.As would be understood by one of ordinary skill, such algorithms woulddepend on the MDI system design criteria and are therefore not fixedparameters for all MDI designs.

The microprocessor is further programmed to perform other desiredfunctions as well, including the provision of messages and alarms viadisplays, speakers or buzzers and tactile warning devices. Programmingfor these functions would also be understood and readily implemented byone of ordinary skill in the art.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be more easily understood with reference to theaccompanying drawings, wherein:

FIG. 1 is a schematic view showing an MDI canister with metered dosevalve and dispensing nozzle and a mouthpiece that attaches to thecanister.

FIG. 2 is a front view of the mouthpiece showing an opening to thedelivery channel and a display.

FIG. 3 is an expanded view of the transfer channel showing a pressuresensing device in operative engagement with the transfer channel of amouthpiece.

FIG. 4 is a circuit diagram for a simplified pressure threshold levelsensor design that is applicable to the basic method of counting doses.

FIG. 5 is flowchart evidencing the logic of a simple dose counter seenin FIG. 4.

FIG. 6 is a circuit diagram for a more complex design that can achievean evaluation of the pressure pulse based on pressure and time data.

FIG. 7 is a flowchart for a dose counter as seen in FIG. 6.

FIG. 8 is a flowchart representing the logic applicable to the use of amotion sensor to determine if a canister has been shaken before use.

DETAILED DESCRIPTION OF THE INVENTION

A Metered Dose Inhaler (MDI) that embodies the present invention is seenin FIGS. 1 and 2 and has two pieces of apparatus, a canister 1 and amouthpiece 2. The canister 1 is typically cylindrical, made of metal andhas a metered dose valve 3 and dispensing nozzle 4 affixed to the top ofthe canister. The mouthpiece 2, usually made of plastic, is manuallymated to the nozzle end of the canister by the patient. The mouthpiece 2comprises a body 5 that is formed with a cylindrical channel 6 forreceiving and firmly holding the canister 1 in an operational position,wherein the nozzle 4 is adjacent a transfer channel 7 formed within themouthpiece. Preferably, the canister 1, cylindrical channel 6, nozzle 4and transfer channel 7 are coaxial and are sized to provide an adequatesealing relationship between the nozzle-end of the canister and thetransfer channel 7 so that upon operation of the valve 4, the dose ofmedicine will not escape at the interface between the canister andmouthpiece.

The MDI dose delivery is actuated by a patient manually squeezing themouthpiece 2 and canister 1 together. A mating structure 8 of themouthpiece 2 engages the nozzle 4 of the canister, causing it to bedepressed as a result of the squeezing force, thereby actuating themetered dose valve. With reference to FIG. 3, the metered dose volume isforced through the valve orifice 9, then through the transfer channel 7that is formed within the channel body 10 of the mouthpiece 2. The dosevolume will exit the transfer channel and enter a delivery channel 11,through which it is directed toward the patient. The dose is forced outof the metered valve 3, not by a "mechanical pump", but due to thepressure developed from the saturated vapor pressure created by thepropellant.

As the dose (a mixture of propellant and medicinal drug) is releasedfrom the pressurized canister, the propellant quickly volatilizes andexpands within the transfer channel 7, causing a pressure burst thatpropels the dose out through the transfer channel exit and into thedelivery channel 11. This pressure rise and fall in the transfer channel7 is sensed by a pressure sensor 12 that is mounted to the body 10 andhas its sensing structure 12A in direct contact with the transferchannel 7.

In the embodiment of FIG. 1 that demonstrates the concept of dosecounting, a miniature solid state (silicon) pressure sensor is affixedto the wall of body 10 with its sensing structure implanted into a holeformed in the body and the tip of the sensing structure flush to theinside wall of the transfer channel 7 of the mouthpiece 2 of an MDIdevice. The pressure sensor 12 may be a Model NPC-109, manufactured byLucas NovaSensor. The sensor is housed in a polycarbonate gel tube andcovered with a dielectric gel (e.g., silicone) in order to protect thesensor from harsh environments, reduce additional volume in the transferpassage and provide a medically acceptable media interface. Pressuresensors are available to measure different pressure ranges, the dynamicpressure range of the sensor in the preferred embodiment being -0.58 psito +5.8 psi, with a sensor response time of 0.8 millisecond. The sensoris electronically connected by a connector 13 to circuitry, as shown inFIG. 4, that includes a microprocessor 14, a Liquid Crystal Display(LCD) 15, and an operational amplifier 16.

As seen in FIG. 4, the pressure sensor 12 may be a silicon device ofconventional technology which reacts to differential pressure, andfunctionally acts as a Wheatstone Bridge 17 (a network of precisionresistors). When a DC voltage is applied across the network inputs (+Vinand -Vin) and pressure differential is zero, resistors are in balanceresulting in a zero voltage difference between the + and - outputs ofthe bridge. When the resistance of one of the resistors is changed dueto change in pressure in the transfer channel, the voltage will deflectin a positive or negative manner reflecting the change.

The outputs of the pressure sensor 12 are applied across the +/- inputsof the operational amplifier 16, along with external pull-up resistor R2and bias resistor R1 act as a voltage comparator. The values of theseresistors are chosen to provide a threshold voltage, (e.g., 35millivolts). Any voltage output from the pressure sensor that is abovethe threshold value would set the output of the operational amplifier tothe "ON state" so as to be "sensed" or "counted" by the microprocessor.Any voltage output from the pressure sensor below the threshold valuewould set the output of the operational amplifier to the "OFF state" soas to be "Not sensed" or "Not counted" by the microprocessor. Any "Notsensed" output from the pressure sensor would drive the output of theoperational amplifier 16 to its minimum value (e.g., 0 Volt).

The operational amplifier 16 converts the very small voltage increasefrom the pressure sensor (e.g., approximately 25 to 65 millivolts) to alarger voltage (e.g., about 5 Volts) output needed to trigger thethreshold (e.g., about 1.4 Volt) for the hi/lo logic input of themicroprocessor 14. The actual voltage output might vary depending on thesource voltage provided (i.e. 3 volts instead of 5 volts).

The microprocessor 14 may be programmed to display the "Remaining Doses"and the "Elapsed Time" from the last dose. The Remaining Doses may bepre-set to 120. The microprocessor 14 would then "Read" the "On" (5volt) or "Off" (0 volt) state of the operational amplifier 16. If the"Off state" is detected, the microprocessor 14 is programmed toincrement an elapsed time counter, redisplay the elapsed time, thenre-read the state of the operational amplifier 16. If the microprocessordetects an "On state", the microprocessor is programmed to decrement theremaining dose count by one, redisplay the "remaining dose", incrementthe elapsed time counter, redisplay the elapsed time, then wait apredetermined "delay time" period before sensing the state of theoperational amplifier again. Preferably, a delay time interval (e.g.,0.75 seconds) is provided to reliably detect a pressure pulse as a dosecount. An insufficient delay time may result in occasional doublecounting because the pulse had not completely been dissipated throughthe transfer channel. Excessively longer delay time intervals couldresult in missed dose counts because the patient would be able tomanually trigger two puffs within the period, even though such quickconsecutive dose administrations would not be recommended by themanufacturer. Tests conducted using a 0.75 second delay time intervalproduced 100% accuracy in counting when 360 doses were administeredevery 5 seconds. No false dose counts were detected when the device wasleft idle for over 5 days.

In a further enhancement of the first embodiment of the invention, abeeping device may be added to the electronic unit of FIG. 4. In thisregard, a miniature speaker device 18 may be connected to one of severalavailable microprocessor outputs and the microprocessor may be preparedto turn the beeper ON or OFF based on the elapsed time or remaining dosecounter status. Thus the patient could be audibly warned when to takethe next dose and/or when the "labeled dose" was imminent.

Finally, the circuit uses a battery 20 as a power supply, the batterybeing small enough to be carried by the mouthpiece 2, together with themicroprocessor 14 and pressure sensor 12.

FIG. 5 illustrates a flowchart for the simple dose counting operation ofthe circuit illustrated in FIG. 4. The microprocessor is initialized atS-100. The dose counter could be either incremented to display the dosesused or decremented to display the doses remaining. In this example, thedisplay of "Remaining Dose" is used; thus, a dose counter in themicroprocessor is set to 120 and the dose counter is decremented eachtime that a dose is detected. The elapsed time since the last dose isset to zero. A delay time parameter is set to 750 milliseconds and thedose count limit is preset to 5 to allow a warning beep when theremaining doses is 5 or less.

In step S-101, the microprocessor displays the current remaining doseand the current elapsed time. Step S-102 concerns the subroutine (SR)processing related to an optional motion sensor application, assubsequently discussed with respect to FIG. 8. The pressure sensor isthen read at step S-103, indicating a value of ON or OFF, based on thecircuit design of FIG. 4. The OFF state represents the state where thereis very little pressure differential above atmospheric pressure(approximately 10% of the peak pulse pressure). The ON state representsa state where the pressure differential is above atmospheric pressure(greater than approximately 10% of the peak pulse pressure). Thethreshold should be high enough so that it cannot be activated by thepatient blowing into the mouthpiece. If the state is ON (S-104), theprogram may wait for a predetermined time at step S-106 to allow thepressure to dissipate. The dose counter is then decremented by one atstep S-107 and the elapsed timer is reset to zero (S-108). If the dosecount is less than the dose count limit (S-109), a beep is activated fora fraction of a second (S-110). The new dose count and elapsed time isthen redisplayed. If the state is OFF (S-104), the program incrementsthe elapsed timer (S-105) and redisplays the dose counter and elapsedtime.

Alternative embodiments may be provided by adding an advanced pressuringsensing capability, by 1) selecting a pressure sensor device withoptimal dynamic pressure range for the designed MDI, and 2) using linearcircuitry techniques to enable the microprocessor to evaluate thepressure pulse in fine detail, as if to model the pressure pulse shape.The microprocessor could be programmed to compare the measured pressurepulse and compare it to a predetermined "desired pulse". Deviationsbetween the measured pressure pulse and desired pressure pulse woulddetermine abnormalities of dose administration, such as 1) a partiallyclogged dispensing path, 2) a leaking canister, 3) inadequate meteringof the dose by the Metering Valve, 4) an abnormal squeezing procedure bythe patient. Such adaptations are available with current pressure sensortechnology and current circuit technology.

The circuit of FIG. 6 includes the arrangement of pressure sensor 12,microprocessor 14, display 15, buzzer 18, motion sensor 19 and batteryas seen in FIG. 4. However, the output of pressure sensor 12 is providedto a linear amplifier 16A, 16B with analog-to-digital converter 17 tosend the digital amplitude measurements to the microprocessor 14. Themicroprocessor fills a data buffer-stack with the pressure pulse streamin the order that measurements are received. Each new pressuremeasurement is added to the top of the buffer stack and the oldest datapoint at the bottom of the stack is lost. The data in the stack at anypoint in time is used to evaluate the state of a dose pressure pulse todetermine if a dose has been administered and to determine if the dosepulse was within designed limits. Knowledge about the desired pressurepulse profile must be preprogrammed into the memory and predictablefaults in MDI operation must be pre-programmed as algorithms. Thesefeatures would be implementable by the programmer having ordinary skillin the art.

The circuit of FIG. 6 can be operated according to the flow chart ofFIG. 7. Specifically, in this approach, the value of the pressure vs.time is measured so as to create a profile of the pressure pulse shapewhich would be used to make more advanced decisions about dose countingand to evaluate the quality of the dose profile and compare it to adesired (ideal) dose profile. The microprocessor is initialized inS-200. The dose counter could be either incremented to display the dosesused, or decremented to display the doses remaining. In this example,the display of the "Remaining Dose" is preferred so the dose counterwould be set to 120 (for example) and the dose counter would bedecremented each time a dose was detected. The elapsed time (since thelast dose) would be set to zero. The delay time referenced in S-209would be set, if needed. The dose count limit in S-213 would be presetto 5 to allow a warning beep when the remaining doses was 5 or less. Anarray of short messages would be pre-programmed into the memory. Thecurrent message value would be pre-set to 0 (no message).

In S-201, the microprocessor would be programmed to display the currentremaining dose, the elapsed time and the current message. S-202 is anoptional motion sensor application (SR) discussed in FIG. 8. Step S-203would be programmed to read the value of the pressure sensor which wouldbe converted to a digital value by the A to D converter 17. The digitalpressure value would then be added to the stack buffer (S-204 andS-206). The data in the Stack buffer (S-206) would then be compared(S-205) to an ideal pressure pulse and also to predictable fault pulsesto make logical decisions about the pressure pulse. Numerous comparisontechniques could be employed. A simple difference between the measuredpulse profile and ideal pulse profile would indicate a "legitimate dose"pressure pulse when the difference was approximately zero. A "cloggedorifice" in the mouthpiece transfer channel would be indicated if thepulse width exceeded the ideal pulse width by approximately 50%. An"almost empty" canister would be indicated by a peak pressure value ofless than approximately 75% of the ideal pulse peak value. A "leaking"canister would be indicated by an approximately constant, slightlyelevated pressure level in the mouthpiece transfer channel. Thisthreshold should be high enough so that it can not be activated by thepatient blowing into the mouthpiece. If the pressure pulse is not alegitimate pulse (S-207) then either a fault pulse would be possible or,the most common situation, no pulse would exist. If it is a fault pulse,then the message would change to indicate the fault. If it were a faultpulse or no pulse, the elapsed time would be incremented (S-208) and thenew dose count, elapsed time, and messages would be redisplayed. If thepulse were a legitimate pulse, the program would wait a pre-defined timedelay (S-209) in order to allow the pressure pulse to completelydissipate (this delay is optional and may not be needed). The dosecounter would decremented by 1 (S-210) and the elapsed timer would resetto zero (S-211). All data in the stack buffer would be cleared (S-212).If the dose count was less than the dose count limit, the beep would beactivated for a fraction of a second (S-214). The new dose count,elapsed time, and messages are then redisplayed.

A further feature of the first and second embodiments is the addition ofa motion sensor 19, which may detect the shaking motion of the MDI,where it is required to shake the contents a predetermined amount priorto use. The signal generated by the motion sensor may be input to themicroprocessor 14 for detection and processing, and for the activationof a display or audible signal to signify that the proper amount ofshaking has been provided.

The operation of the microprocessor using the miniature motion sensor isseen in the flowchart of FIG. 8 where the motion sensor is read (S-300)to determine (S-301) if the sensor is in motion, i.e., beyond athreshold of time and/or magnitude. The threshold is programmed so as toavoid detection of ordinary handling, but would detect shaking of anadequate amount and/or for an adequate period of time. If the minimumamount of motion (time/magnitude) was detected, the motion timer wouldbe reset to zero (S-306) and the process would proceed as in FIGS. 5 and7 and continue to cycle through the steps as appropriate. If motion werenot detected, the motion timer would increment its current count(S-302). If the motion timer is less than a predetermined period oftime, the minimum amount of shaking would have been provided and themessage would be "ready" (S-305). If the motion timer is greater than apredetermined time, e.g., 60 seconds, the canister would have been atrest for a period sufficient to have the contents separate and a minimumamount of shaking would again have to be provided, thus the messagewould be "shake before using".

When implementing the dosage counter, the MDI should not be designed tolock when it reached the labeled number of actuations. Rather, it shouldbeep and/or display a warning message during the last five or otherselected number of actuations since locking of the dosage form may causea problem during an acute asthmatic attack. During such an attack,bronchodilators administered in less than labeled doses would be of somerelative benefit compared to no dose being available at all. Furtheradvanced evolution of the invention could permit an assessment of thepatient's pulmonary status following delivery of the drug. The inventioncould also contain different auditory warnings, for example, indicatingwhether or not the patient inspired forcefully enough.

MDI technology also can be used to administer doses to the nasalpassages and it is to be understood that nasal dose applications are inthe spirit and scope of this invention. In fact, even topicalapplications using a pressure delivery system can be monitored andrelevant information displayed.

While the present invention has been illustrated and described withrespect to preferred embodiments, it is not intended to be therebylimited. It would be understood by one of ordinary skill in the art thatvarious omissions; modifications, substitutions and changes can be madewith respect to the details of any device that implements the invention,without departing from the spirit of the present invention, as set forthin the appended claims.

We claim:
 1. A drug dispensing apparatus comprising:a pressurizedcontainer for a dispensable drug, said container comprising at adelivery end a metered dose valve and a nozzle, said nozzle at its exitproviding a metered dose at a predetermined pressure when said metereddose valve is actuated; a delivery apparatus comprising a transferpassage and a delivery passage, said transfer passage being incommunication with said nozzle exit for receiving a metered dose of saiddrug substantially at said predetermined pressure, and a pressure sensorfor detecting the changes in pressure in said transfer passage.
 2. Thedrug dispensing apparatus as set forth in claim 1 further comprisingmeans responsive to said pressure sensor for providing informationconcerning said drug delivery process.
 3. The drug dispensing apparatusas set forth in claim 2 wherein said responsive means comprises amicroprocessor in communication with said pressure sensor and a display.4. The drug dispensing apparatus as set forth in claim 2 wherein saidresponsive means comprises a microprocessor in communication with saidpressure sensor and an audible announcer apparatus.
 5. The drugdispensing apparatus as set forth in claim 2 wherein said responsivemeans comprises a microprocessor in communication with said pressuresensor, said microprocessor being operative to count the number of timesthe pressure exceeds a predetermined threshold level.
 6. The drugdispensing apparatus as set forth in claim 2 wherein said responsivemeans comprises a microprocessor in communication with said pressuresensor, said microprocessor being responsive to at least one of theduration and magnitude of pressure detected by said pressure sensor fordetermining the existence of pressure pulses.
 7. The drug dispensingapparatus as set forth in claim 6 wherein said microprocessor countsdown from a predetermined number.
 8. The drug dispensing apparatus asset forth in claim 6 wherein said responsive means is operative toprovide information at least at a predetermined count.
 9. The drugdispensing apparatus as set forth in claim 1 wherein said deliveryapparatus comprises a mouthpiece having a cylinder engagement chamberfor sealingly receiving said delivery end of said container.
 10. Thedrug dispensing apparatus as set forth in claim 1 wherein said containercomprises a cylindrical canister having an outer circumferentialdimension at said delivery end, and said delivery apparatus comprises acylindrical channel for sealingly receiving said canister delivery end.11. The drug dispensing apparatus as set forth in claim 1 furthercomprising a motion detector for detecting a shaking applied to saidapparatus and means responsive to said motion detector for determiningwhether said shaking action satisfies predetermined criteria.
 12. Adelivery apparatus for use with a pressurized container having a metereddose valve and a nozzle for emitting metered doses of a drug, saidnozzle at its exit providing a metered dose at a predetermined pressurewhen said metered dose valve is actuated, said apparatus comprising:abody comprising a structure for interfacing with said pressurizedcontainer; a transfer passage for communication with said nozzle exitfor receiving a metered doses of said drug substantially at saidpredetermined pressure; a pressure sensor for detecting the changes inpressure in said transfer passage; and a delivery passage incommunication with said transfer passage for providing said metered doseof said drug to a patient.
 13. The drug dispensing apparatus as setforth in claim 12 further comprising a display and means responsive toan output of said pressure sensor for indicating a metered dosecondition by said display.
 14. The drug dispensing apparatus as setforth in claim 12 further comprising an audible announcer and meansresponsive to an output of said pressure sensor for indicating a metereddose condition by said announcer.
 15. A method of monitoring thedelivery of a metered dose from a pressurized container via a mouthpiecehaving a transfer passage for directing said metered doses from thecontainer to the patient comprising:detecting dosage-related pressureincreases in said transfer passage; counting doses on the basis of thenumber of times that said pressure increases are detected; and providinginformation in response to said counting step.
 16. The method ofmonitoring as set forth in claim 15 further comprising detecting motionof said container and providing information in response to said motiondetecting step.
 17. The method of monitoring as set forth in claim 15wherein said counting step comprises counting down from a predeterminednumber.
 18. The method as set forth in claim 15 wherein said step ofproviding information comprises generating a visual message display. 19.The method as set forth in claim 15 wherein said step of providinginformation comprises generating an audible message.
 20. The method asset forth in claim 15 further comprising the step of detecting a minimumamount of shaking and said providing information step further comprisesproviding information concerning said shaking step.
 21. The drugdispensing apparatus of claim 1 wherein said pressure sensor has asensing portion disposed for directly sensing pressure changes in saidtransfer passage.
 22. The delivery apparatus of claim 12 wherein saidpressure sensor has a sensing portion disposed for directly sensingpressure changes in said transfer passage.